Thermally enhanced semiconductor device utilizing a vacuum to ultimately enhance thermal dissipation

ABSTRACT

A semiconductor device having a heat sink is provided in which an opening through the heat sink enables a vacuum source to be applied to a semiconductor die mounted surface. In one form, a semiconductor die is attached to a mounting surface of a leadframe. The leadframe also has a plurality of leads which are electrically coupled to the semiconductor die. The semiconductor die and portions of the leads encapsulated in a package body. Also incorporated in the package body is a heat sink. The heat sink has an opening which extends through the heat sink and exposes a portion of the mounting surface of the leadframe. The opening is used to apply a vacuum to the mounting surface during the formation of the package body so that the mounting surface and heat sink are held in close proximity. The closeness provides a good thermal conduction path from the semiconductor die to the ambient, thereby enhancing the thermal dissipation properties of the device.

CROSS-REFERENCE TO RELATED APPLICATION

Related subject matter is disclosed in U.S. patent application Ser. No.07/519,375 entitled "Semiconductor Device Having an Insertable Heat Sinkand Method for Mounting the Same", filed May 3, 1990 and assigned to theassignee hereof.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to semiconductor devices in general, andmore specifically to thermally enhanced semiconductor devices and theencapsulation of such devices.

BACKGROUND OF THE INVENTION

An increase in the power consumption of semiconductor devices has led toa need for semiconductor packages which have a lower thermal resistance.In general, the plastics and ceramics commonly used to packagesemiconductor devices do not dissipate heat sufficiently for some typesof devices. Examples of devices requiring good heat dissipation includefast static RAMs (random access memories), gate arrays, andmicroprocessors. One of the most common and effective approaches togreater thermal dissipation in semiconductor devices is the addition ofa heat sink, or heat spreader, to the package. A heat sink is typicallymade of a material having a high thermal conductivity, such as copper,and ideally would be in good thermal contact to the semiconductor die,would have a surface which is exposed to the ambient, and would have amaximized surface area.

Heat sinks used in semiconductor devices have taken many forms. Heatsinks may have irregular topographies, such as channels or grooves, toincrease the exposed surface area of the heat sink, thereby improvingthermal dissipation. In addition, a number of materials have been usedas heat sink materials, including copper, copper alloys, copper-tungstenalloys, aluminum, aluminum alloys, molybdenum, and composites of thesematerials. Other features of heat sinks which have been used in the pastare features which improve the adhesion of the heat sink to asemiconductor package. In the case of plastic semiconductor packages,using a heat sink may result in poor adhesion between the plasticencapsulating material and the heat sink. To overcome this problem,semiconductor manufacturers have used heat sinks having features such asdimples, holes, or roughened surfaces to achieve better adhesion.

Apart from achieving sufficient adhesion between a heat sink and apackage body material, other problems of incorporating a heat sink intoa semiconductor device exist. In the assembly of plastic semiconductordevice packages, it is possible to incorporate a heat sink during thesemiconductor die bonding operation, during the molding of the packagebody, or a heat sink may be attached after the package body is formed.However, a variety of manufacturing difficulties exist with each ofthese techniques.

To include a heat sink during a die bonding operation, a semiconductordie may be attached directly onto a heat sink which is attached to aleadframe, rather than onto a flag or mounting surface which is alreadypart of the leadframe. While it seems reasonable to mount a die directlyonto a heat sink in order to achieve good thermal conduction from thedie to the heat sink, the added weight of the heat sink on a leadframecan cause substantial damage to the leadframe due to handling. Moreover,some of the equipment used in subsequent assembly operations may need tobe modified in order to accommodate the presence of the heat sink on theleadframe.

To incorporate a heat sink within a device during the molding of apackage body, the heat sink may be placed directly in a mold tool cavitysuch that it is at least partially encapsulated during the formation ofthe package body. Encapsulating the heat sink while forming the packagebody can have the advantage of achieving a standard package outline.Furthermore, it does not require the addition of an assembly operationto a conventional assembly process flow. A disadvantage associated withthis method is that during the injection of an encapsulation materialinto the cavity, the heat sink is often moved, causing it to bemisaligned within the package. There is also a risk that the heat sinkwill become completely encapsulated, thereby leaving no exposed surfacefrom which to dissipate heat. Another disadvantage is that it isdifficult to achieve good thermal contact between the heat sink and thesemiconductor die. Air or the encapsulation material may be trappedbetween the heat sink and the die, thus increasing the overall thermalresistance of the device.

Incorporating a heat sink after package body is formed generallyinvolves attaching a heat sink to the exterior of the package throughthe use of an adhesive material, such as a thermally conductive epoxy.However in doing so, the heat sink is positioned away from the die suchthat good thermal conduction away from a semiconductor die to the heatsink is obstructed by the package body material and any voids whichmight be present in the material. Along with the disadvantage of nothaving the heat sink in good thermal contact with the die, there is alsoa disadvantage of having a non-standard package outline. Furthermore, anattached heat sink increases the overall size of a semiconductor devicewhich is an undesirable feature to most end users of semiconductordevices. Therefore a need existed for an improved thermally enhancedsemiconductor device which can be readily manufactured with minimalmodifications to conventional assembly equipment and which maintains theoutline of a standard package.

BRIEF SUMMARY OF THE INVENTION

There is provided, in accordance with the present invention, asemiconductor device having enhanced heat dissipation ability whichachieves these and other advantages. In one form, a semiconductor diehaving a plurality of bonding pads thereon is attached to a mountingsurface of a leadframe. Along with a mounting surface, the leadframealso has a plurality of leads which are electrically coupled to thebonding pads of the semiconductor die. The semiconductor die andproximal ends of the plurality of leads are encapsulated in a packagebody such that a first portion of the mounting surface of the leadframeis exposed. A heat sink, having an opening therein which extends throughthe heat sink, is positioned such that an outer surface of the heat sinkis substantially exposed, and an inner surface of the heat sink isadjacent to the mounting surface of the leadframe. The opening throughthe heat sink exposes a second portion of the mounting surface andenables a vacuum to be applied to the mounting surface in order to havethe mounting surface and heat sink in close proximity duringencapsulation of the device.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of a thermally enhanced semiconductordevice, in accordance with the present invention.

FIG. 2 is a cross-sectional view of a semiconductor device illustratinganother embodiment of the present invention.

FIG. 3 is a cross-sectional view of a mold tool which illustrates amethod of forming a semiconductor device, in accordance with the presentinvention.

FIG. 4 is a perspective illustration of another form of a thermallyenhanced semiconductor device, also in accordance with the presentinvention.

FIG. 5 is a perspective illustration of another embodiment of thepresent invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

With the present invention, it is possible to meet the previously stateddesired features of a thermally enhanced device. The invention enables aheat sink within a semiconductor device to be in the thermal path of asemiconductor die and to have a maximized surface area which is exposedto the ambient. Moreover, the invention provides a method formanufacturing such a device. A semiconductor device 10, in accordancewith the invention, is illustrated in FIG. 1. A semiconductor die 12 isattached to a mounting surface 14 of a leadframe 16 (not entirelyshown), typically by use of a conductive adhesive material such as aconductive filled epoxy. Leadframe 16 is also made of a conductivematerial such as copper, a copper alloy, an iron-nickel alloy, or othermetals. The leadframe may also be a TAB (tape automated bonding) tapewhich is commonly used in the art. Leadframe 16 has a plurality of leads18 which each have ends proximal and distal to semiconductor die 12. Theleads are electrically coupled to the die. As illustrated, wire bonds 20are used to couple proximal ends of leads 18 to bonding pads (not shown)on semiconductor die 12. Wire bonds 20 are of a conductive material suchas gold, copper, aluminum, or alloys of these materials. Other couplingmethods, such as the use TAB bonds, may also be employed.

As illustrated in FIG. 1, the semiconductor die 12, the proximal ends ofthe leads, the wire bonds 20, and portions of the mounting surface 14are encapsulated by a package body 22. Package body 22 is typically madeof a molded plastic material, for example a phenolic epoxy, an epoxynovolac resin, or other molding compound resin. Distal ends of leads 18extend out of package body 22 and are formed in a gull-wingconfiguration. The distal ends of the leads may also be formed intoother lead configurations, such as a J-lead or a through-holeconfiguration. Semiconductor device 10 also has a heat sink 24 which maybe of a conventional heat sink material, such as copper, a copper alloy,a copper-tungsten alloy, aluminum, an aluminum alloy, molybdenum, or acomposite of these materials. Heat sink 24 has an outer and an innersurface. The inner surface of heat sink 24 is in contact with mountingsurface 14, and therefore can effectively conduct heat away fromsemiconductor die 12. Although not shown in FIG. 1, a thermallyconductive, adhesive material may be incorporated between the innersurface of heat sink 24 and mounting surface 14. The addition of anadhesive material will aid in keeping the heat sink and mounting surfacein close proximity. In addition, use of an adhesive material will helpprevent contaminants from entering into device 10 and causing harm tosemiconductor die 12. Adhesive materials suitable for use with thepresent invention include materials commonly used to bond asemiconductor die to a mounting surface, such as a thermally conductiveepoxy or solder. The outer surface of heat sink 24 is exposed to theambient, thus providing a large surface area through which heat isremoved from device 10. The outer surface of the heat sink 24 is flushwith the outer surface of package body 22, allowing device 10 to havethe advantage of a standard package outline. The heat sink may alsoinclude locking features, such as 27 and 28, which help secure heat sink24 to package body 22 and help maintain good thermal contact betweenheat sink 24 and semiconductor die 12. As mentioned in the backgroundsection, such locking features are known in the art.

An opening 26 through the heat sink 24 illustrated in FIG. 1 isincorporated as a manufacturing aid, but also has other advantages.During the formation of package body 22, opening 26 is used to provide avacuum to mounting surface 14. The reason for applying a vacuum is toassure that mounting surface 14 and heat sink 24 are held in closeproximity during the encapsulation of semiconductor die 12. Having thesetwo elements in close contact during the encapsulation process reducesthe tendency for any of the encapsulation material to seep between themounting surface 14 and the heat sink 24. Furthermore, having a vacuumapplied to the mounting surface helps to hold the heat sink against themold tool cavity, thereby preventing misalignment of the heat sinkduring the introduction of the encapsulating material. Having the heatsink held closely to the mold tool cavity also prevents theencapsulation material from seeping over the outer surface of the heatsink. An encapsulation process in accordance with the present inventionwill be described in more detail in the discussion of FIG. 3. The sizeof opening 26 may be optimized in order to achieve a desired pullingforce on mounting surface 14; however, opening 26 is typically of suchsize that it is substantially visible.

Besides aiding in the manufacturing of a thermally enhancedsemiconductor device, opening 26 also allows moisture to escape from thedevice. The addition of an opening in a semiconductor package for thepurpose of releasing moisture is taught by Nambu et al. in U.S. Pat. No.4,866,506, filed Jan. 29, 1987, and entitled "Plastic-Sealed IC Deviceof Heat Resistant Construction". A common problem in plasticsemiconductor packages is that the plastic packages absorb and retainmoisture. This problem is particularly harmful for surface mountpackages. Due to the high temperatures and rapid temperature changes ofthe surface mount process (i.e. mounting the device to a substrate, suchas a printed circuit board), the moisture in the package vaporizes,causing the package to crack. This is often referred to as "popcorncracking". By having a hole in the heat sink, a vent is created fromwhich the moisture may easily escape without damaging the package.

Illustrated in a cross-sectional view in FIG. 2 is an alternativeembodiment of the invention. This embodiment is very similar to theprevious embodiment with modifications to the heat sink shape, the shapeof the locking features and the lead configuration. Device 10' is madeup of a semiconductor die 12', a leadframe 16' (not entirely shown)having a mounting surface 14' and a plurality of leads 18', wire bonds20' which electrically couple leads 18' to die 12', a package body 22',and a heat sink 31. Elements in this illustration are analogous to thecorresponding elements of FIG. 1. The heat sink 31 in this embodimenthas protrusions, such as protrusion 29. Protrusion 29 increases theexposed surface area of the heat sink, thereby increasing the amount ofheat which is dissipated from device 10. The protrusions, includingprotrusion 29, are illustrated in cross-section as being squarefeatures, although any shape which increases the exposed surface area ofthe heat sink over the planar area is acceptable for use with thepresent invention. The manufacture of device 10' of FIG. 2 might requireadditional tooling modification to accomodate the presence of anyprotrusions. Heat sink 31 also has an opening 30 which extends throughthe heat sink, exposing the mounting surface 14' as in the previous formof the invention.

Another difference in the embodiment illustrated in FIG. 2 is the shapeof the locking features, 32 and 34 respectively, used in the heat sink.These features are filled with the encapsulating material and hold theheat sink in place within the package body. Locking features are notnecessary to the invention; however, the use of locking features helpsto ensure that the heat sink remains in contact with the mountingsurface and that the heat sink does not become removed from the package.As in the previous embodiment, a thermally conductive adhesive materialmay also be incorporated between the inner surface of heat sink 31 andmounting surface 14' to further ensure that the heat sink and mountingsurface remain in close proximity. The configuration of leads 18' isalso different from the previous embodiment. As illustrated in FIG. 2,leads 18' are formed into a J-lead configuration, rather than thegull-wing configuration of FIG. 1. While the J-lead and gull-wingconfigurations are conventionally used for surface mount packages,through-hole configurations may also be used in conjunction with thepresent invention.

Also in accordance with the present invention is a method for forming athermally enhanced semiconductor device. During a conventional moldingprocess of a plastic semiconductor package, a leadframe with asemiconductor die attached and electrically coupled thereto is placed onone of two mold tool platens. The two platens are then brought togetherto form a cavity around the die and proximal ends of the leads. Anencapsulating material is introduced into the cavity, thereby forming apackage body.

With the present invention, a heat sink is also encapsulated during theformation of a package body. As illustrated in FIG. 3, a mold tool 40has an upper and a lower platen, 41 and 42 respectively. A heat sink 38is positioned in lower platen 42 of a mold tool 40. If desired, athermally conductive adhesive material may be applied to the heat sinkeither before or after positioning the heat sink in the mold tool. Theinclusion of such an adhesive material will aid in keeping the heat sinkin close proximity to a semiconductor die mounting surface 44. Heat sink38 has an opening which extends through the heat sink and is aligned toa first vacuum source, in this case vacuum line 100 within platen 42(the vacuum source will be described in more detail at a later point). Aleadframe (not entirely shown) is positioning and aligned on mold toolplaten 42. The leadframe has mounting surface 44 and a plurality ofleads 45. A semiconductor die 46 is attached to the mounting surface 44and is electrically coupled to leads 45 by wire bonds 47. The leadframeis positioned such that mounting surface 44 covers vacuum line 100 andsuch that mounting surface 44 overlies heat sink 38. If using athermally conductive adhesive material between the mounting surface andthe heat sink, the adhesive material may be applied to the mountingsurface, rather than to the heat sink. Platens 41 and 42 are broughttogether to form a cavity 49 around the semiconductor die 46, mountingsurface 44, wire bonds 47, and proximal ends of leads 45. Anencapsulating material (not shown) is then introduced into cavity 49,thus forming a package body about the semiconductor die. Anyencapsulating material typically used in forming semiconductor packages,such as a novalc epoxy resin or other polymers, is suitable for use withthe present invention.

In one form of the present invention, one of two mold tool platens ismodified to include at least one vacuum source, unlike most conventionalplatens. While some mold tools on the market include a vacuum source,the vacuum in these tools is typically used to evacuate air from each ofthe mold tool cavities. By removing air from the cavities, there is areduced probability that a void will be formed in the package bodyduring the encapsulation process. Voiding is particularly a problem whenthe cavities are thin and when there is insufficient venting in the moldtool. Vacuum technology has also been used in one-sided molding in whicha semiconductor die is molded directly onto a substrate, such as aprinted circuit board. In the one-sided molding application, the vacuumis used to hold the substrate in place while an upper platen is placedover the substrate and a package is formed around the die. Vacuumtechnology has also been used to hold an over-molded substrate in placeduring encapsulation to control unwanted molding material, also known asflash, from covering certain portions of the substrate. For example, useof a vacuum to control flash on a printed circuit board (PCB) in anover-molded pin grid array (OMPGA) package is taught in an article by M.McShane et al., entitled, "A Unique Low Cost Pin Grid Array Package withHeatspreader", which was published in the Proceedings of the NinthAnnual International Electronics Packaging Conference, Sept.11-13,1989,pp.199-207.

As illustrated in FIG. 3 in accordance with the present invention, twovacuum sources are included in platen 42. Vacuum line 100 is used topull a vacuum (or partial vacuum) on mounting surface 44 of theleadframe (not shown entirely). The opening through heat sink 38provides a path from vacuum line 100 to mounting surface 44. This vacuumis used to ensure that mounting surface 44 is held in close proximity toheat sink 38 to substantially prevent any encapsulating material frompenetrating between these elements. The addition of a thermallyconductive adhesive material on the inner portion of the heat sinkfurther ensures that the heat sink and mounting surface are held inclose proximity. By having mounting surface 44 and heat sink 38 in closeproximity, the heat dissipation away from semiconductor die 46 isimproved over devices which have encapsulating material separating thedie and the heat sink. A second vacuum source, vacuum line 200, may beused to pull a vacuum (or partial vacuum) on heat sink 38. Althoughvacuum line 200 is not a necessary element of the invention, it isincluded in this embodiment as an additional manufacturing aid. Vacuumline 200 secures heat sink 38 to the mold platen 42 such that asignificant portion of the encapsulating material cannot enter betweenthe heat sink and platen. In doing so, what is to be the exposed portionof the heat sink is protected from being covered by the encapsulatingmaterial. Upon formation of the package body, the maximum surface areaof the heat sink will be exposed to the ambient, thus establishing anoptimal condition for thermal dissipation of the device. As mentionedabove, using a vacuum to control flash in a thermally enhancedsemiconductor device is known and can be used in conjunction with thepresent invention as a manufacturing aid. Securing the heat sink to theplaten through the use of a vacuum also prevents misalignment of theheat sink during the introduction of the encapsulating material into thecavity.

The vacuum sources illustrated in FIG. 3 are tubular; however, theconfiguration of the vaccum source may be modified. For instance, theportion of the source which is next to either the heat sink or mountingsurface may be enlarged in order to have a stronger pulling force on theelement. Another method of increasing the pulling force is to configurethe vacuum source in a ring shape which will increase the area of theheat sink or mounting surface under vacuum. Furthermore, the two sourcesillustrated in FIG. 3 might be combined into one vacuum source to reducetooling modification costs and complexity.

A perspective view of a semiconductor device in accordance with theinvention is illustrated in FIG. 4. A semiconductor device 50 has a heatsink 52 which is used to dissipate heat from a semiconductor die (notshown). The semiconductor die is attached to a mounting surface 54 of aleadframe (not entirely shown). The mounting surface 54 is visiblethrough an opening 56 which extends through heat sink 52. Opening 56 isprovided in order to apply a vacuum to mounting surface 59 during theformation of a package body 58. By applying a vaccum to the mountingsurface, mounting surface 54 and heat sink 56 are held closely togetherduring the encapsulation of the semiconductor die. Upon forming packagebody 58, heat sink 52 and mounting surface 54 remain in close proximity,such that a good thermal path exists from the semiconductor die to theheat sink, and therefore to the ambient.

Also within the heat sink 52 illustrated in FIG. 4 are locking features60. Unlike the locking features of previous embodiments, lockingfeatures 60 are located near each corner of heat sink 52. The number andposition of locking features 60 which might be used with the presentinvention need not be as illustrated in FIG. 4. Rather, a sufficientnumber and location of locking features to ensure that heat sink 52 isheld securely in the package body and in close proximity to mountingsurface 54 is desirable. The shape of locking features 60 may also bemodified to best meet the needs of a particular semiconductor device.The locking features 60 extend through heat sink 52 such that theencapsulating material used to form package body 58 is visible. Thelocking features used need not extend entirely through the heat sink.For an example of such locking features, refer to FIG. 2. For the deviceof FIG. 2, the encapsulating material would not be visible at the outersurface of the heat sink because the locking features do not extendthrough the exposed surface of the heat sink. While the use of lockingfeatures in conjunction with the present invention has been discussed ingreat detail, it is important to note that the use of locking featuresmay not be necessary. A heat sink surface may adhere to a package bodysufficiently by use of other adhesion promoters such that lockingfeatures are not needed.

Heat sink 52 is illustrated as having a rectangular shape in FIG. 4.Package body 58 is also rectangular, such as the package bodies of PLCCs(plastic leaded chip carriers) or QFPs (quad flat packs). Byincorporating a rectangular heat sink in a rectangular package body, amaximized exposed heat sink surface area can be achieved. However, asmentioned earlier, the shape of the heat sink may be modified to meetother device or manfacturing requirements. Other possible heat sinkshapes include rectangular, square, circular, oval, or an irregulargeometric shape.

Illustrated in FIG. 5 is another perspective view of a semiconductordevice 70 which is also in accordance with the present invention. Inthis embodiment, the device has two semiconductor die (not shown) whichare attached to two mounting surfaces, 77 and 78. Only a portion of themounting surfaces are visible, but the remaining portions of themounting surfaces are represented in the figure by dotted lines A and B.Because device 70 has two mounting surfaces, a heat sink 72 has twoopenings 75 and 76 which extend through heat sink 72. Openings 75 and 76are provided in order to apply a vacuum to mounting surfaces 77 and 78,respectively, during the formation of a package body 74. Similarly, twoseparate heat sinks might be used in device 70, as opposed to one heatsink having two openings as illustrated. Furthermore, a semiconductordevice may have any number of semiconductor die, any number of mountingsurfaces, and any number of heat sinks and be in accordance with thepresent invention.

The present invention provides a low cost, easy to manufacturesemiconductor device having a heat sink. The inventive device meetsoptimal conditions of a thermally enhanced device, namely a heat sinkwhich is in the direct thermal path of low thermal resistance with thesemiconductor die and has a maximized surface area which is exposed tothe ambient. In addition to these optimal conditions, the presentinvention also provides the opportunity to have a standard packageoutline for the device. The presence of an opening through a heat sink,in accordance with the present invention, permits a vacuum to be appliedto a mounting surface of a leadframe in order to hold the mountingsurface in close proximity to the heat sink during the formation of apackage body. The close proximity between these elements is necessary inorder to provide an optimal thermal path from a semiconductor die to theambient. The presence of the opening has the additional advantage ofallowing any moisture within the package to escape during boardmounting, thereby preventing the package from cracking. The inventionrequires minimal tooling modification to conventional assemblyequipment; therefore, the cost of assembling the device is kept low.Only one tooling modification is essential, that being the addition ofat least one vacuum source to the mold tool which is used to hold themounting surface and heat sink in close proximity during the formationof the package body. An additional benefit achieved by using a vacuumsource in a mold tool is that the vacuum may also be used to remove airfrom the mold cavity prior to introducing an encapsulating material.Furthermore, after the package body has been formed, air can be forcedthrough a vacuum line to assist in ejecting a device from the cavity.

Thus it is apparent that there has been provided, in accordance with theinvention, a thermally enhanced semiconductor device and method forforming the same that fully meets the advantages set forth previously.Although the invention has been described and illustrated with referenceto specific embodiments thereof, it is not intended that the inventionbe limited to these illustrative embodiments. Those skilled in the artwill recognize that modifications and variations can be made withoutdeparting from the spirit of the invention. For example, use of theinvention is not limited to use in conjunction with semiconductordevices having only one semiconductor die but may be used with multipledie devices. The invention is not limited to using the materialsmentioned for the various elements of the invention, but may include useof any material which meets the needs of that particular element. Nor isthe invention limited to using the heat sink configuration illustratedor described. Any heat sink having an opening through which a vacuum isapplied may be used and is considered to be within the scope of theinvention. Furthermore, it is not intended that the invention be limitedto the use of only one heat sink. Therefore, it is intended that thisinvention encompass all such variations and modifications as fall withinthe scope of the appended claims.

We claim:
 1. A thermally enhanced semiconductor device, comprising:aleadframe having a mounting surface and a plurality of leads havingproximal and distal ends; a semiconductor die attached to the mountingsurface, the semiconductor die having a plurality of bonding padselectrically coupled to the plurality of leads of the leadframe; a heatsink having a predetermined perimeter, an outer surface which issubstantially exposed, and an inner surface which is adjacent to themounting surface of the leadframe; a package body encapsulating thesemiconductor die and partially encapsulating the heat sink; and anopening through the heat sink which is displaced from the perimeter ofthe heat sink, the opening exposing a portion of the mounting surfaceand providing a means for applying a vacuum to the exposed portion ofthe mounting surface in order to have the mounting surface and heat sinkin close proximity during encapsulation of the device to enhance thermaldissipation from the mounting surface to an ambient during deviceoperation.
 2. The semiconductor device of claim 1 wherein the packagebody is made from a molding compound resin.
 3. The semiconductor deviceof claim 1 wherein the heat sink comprises a material selected from thegroup consisting of copper, copper alloys, copper-tungsten alloys,molybdenum, aluminum, aluminum alloys, and composites of thesematerials.
 4. The semiconductor device of claim 1 wherein the packagebody further comprises an outer surface and wherein the outer surface ofthe heat sink and the outer surface of the package body aresubstantially coplanar.
 5. The semiconductor device of claim 1 whereinthe heat sink further comprises a locking means for holding the heatsink in place.
 6. The semiconductor device of claim 1 wherein the heatsink has a shape selected from the group consisting of rectangular,square, circular, and oval.
 7. The semiconductor device of claim 1wherein the heat sink has at least one side having two portions whichare positioned at differing angles with respect to an adjacent side ofthe package body.
 8. The semiconductor device of claim 1 wherein theopening is of such a size that the opening is substantially visible. 9.A thermally enhanced semiconductor device, comprising:a leadframe havinga plurality of mounting surfaces, each having an associated plurality ofleads having proximal and distal ends; a semiconductor die attached toeach of the mounting surfaces, the semiconductor die having a pluralityof bonding pads electrically coupled to the plurality of leadsassociated with each mounting surface; a heat sink having apredetermined perimeter, an outer surface which is substantiallyexposed, and an inner surface which is adjacent to each of the mountingsurfaces of the leadframe; a package body encapsulating all of thesemiconductor die and partially encapsulating the heat sink; and aplurality of openings through the heat sink corresponding in number tothe plurality of mounting surfaces, the openings being displaced fromthe perimeter of the heat sink, exposing a portion of each of themounting surfaces, and providing a means for applying a vacuum to eachof the exposed portions of the mounting surfaces in order to have theplurality of mounting surfaces held in close proximity to the heat sinkduring encapsulation of the device to enhance thermal dissipation fromeach of the mounting surfaces to an ambient during device operation. 10.The semiconductor device of claim 9 wherein the heat sink comprises amaterial selected from the group consisting of copper, copper alloys,copper-tungsten alloys, molybdenum, aluminum, aluminum alloys, andcomposites of these materials.
 11. The semiconductors device of claim 9wherein the package body further comprises an outer surface and whereinthe outer surface of the heat sink and the outer surface of the packagebody are substantially coplanar.
 12. The semiconductor device of claim 9wherein the heat sink further comprises a locking means for holding theheat sink in place.
 13. The semiconductor device of claim 9 wherein eachof the plurality of openings are of such size that the openings aresubstantially visible.
 14. The semiconductor device of claim 9 furthercomprising a thermally conductive material which adhesively couples theinner surface of the heat sink to each of the mounting surfaces of theleadframe.
 15. A thermally enhanced semiconductor device, comprising:aleadframe having a mounting surface and a plurality of leads havingproximal and distal ends; a semiconductor die attached to the mountingsurface, the semiconductor die having a plurality of bonding padselectrically coupled to the plurality of leads of the leadframe; a heatsink having a predetermined perimeter, an outer surface which issubstantially exposed, and an inner surface which is adjacent to themounting surface of the leadframe; a thermally conductive materialadhesively coupling the inner surface of the heat sink to the mountingsurface of the leadframe; a package body encapsulating the semiconductordie and partially encapsulating the heat sink; and an opening throughthe heat sink which is displaced from the perimeter of the heat sink,the opening exposing a portion of the mounting surface and providing ameans for applying a vacuum to the exposed portion of the mountingsurface in order to have the mounting surface and heat sink in closeproximity during encapsulation of the device to allow the thermallyconductive material to adhesively and thermally couple the inner surfaceof the heat sink to the mounting surface of the leadframe, therebyenhancing thermal dissipation from the mounting surface to an ambientduring device operation.